This invention relates to a laser beam machining process and an apparatus therefor, more particularly to a novel laser beam machining process and an apparatus, for the machining of a work piece such as of an impression material comprising a rubbery material typified by natural rubbers and elastomers to form seals or stamps, which can provide a printing face with increased strength and improve ink permeability in porous materials to overcome printing nonuniformity.
In a conventional laser beam machine of the structure schematically shown in FIG. 12, a work piece 5 comprising a rubbery material typified by a natural rubber or elastomer and a model to be scanned 6 (scanning model) having a pattern depicted thereon such as letters and the like to be carved on the surface of the work piece 5 are placed on a work table 7. A pattern sensor 8 is disposed above the scanning model 6, whereas a laser beam generator comprising a laser energy source g and a laser oscillator 10 is disposed above the work piece 5. The work table 7 which is designed to be driven by a reciprocator (not shown) is reciprocated sequentially in a horizontal direction relative to the pattern sensor 8 and the laser oscillator 10, whereupon the pattern sensor 8 detects the pattern depicted on the scanning model 6 as it passes directly below the sensor 8.
During the time when the sensor 8 is not detecting the pattern (i.e. when the sensor 8 is scanning the white ground of the scanning model 6 having a black pattern depicted thereon), a signal detecting the white ground is transmitted to the laser energy source 9, and the laser energy source 9 energizes the laser oscillator 10 to give 100% output. Accordingly, the laser beam irradiated from the laser oscillator 10 is reflected on a reflector 11 to impinge upon the surface of the work piece 5, whereby counters are carved as the work table 7 is reciprocated sequentially. On the other hand, when the scanning by the sensor 8 transits from the white ground to the black portion, a signal detecting the black portion is transmitted from the sensor 8 to the laser energy source 9, whereupon the laser irradiation onto the surface of the work piece 5 is interrupted. By repeating the feeding motion of the work table 7, per one cycle of the horizontal reciprocating motion thereof, in the horizontal direction orthogonal to the reciprocating direction, the surface of the work piece 5 is carved taking exactly or approximately after the pattern depicted on the scanning model 6.
FIG. 10 shows, in cross section, protrusions 1 formed, according to a conventional technique such as hand carving or plate making, on the surface of a work piece comprising a rubbery material such as a natural rubber or elastomer for making a seal or stamp. As shown in FIG. 10, the bottom width of the protrusions 1 is made wider than the top width on which an ink including vermilion seal-ink is applied; in other words the protrusions have a trapezoidal cross section. The reason is to improve the physical strength of the protrusions 1 to prevent damage thereof and extend the life of the machined work piece since the rubbery material is soft unlike hard work pieces such as ivory.
On the other hand, FIG. 11 shows also, in cross section, protrusions 2 formed, according to the conventional laser beam machine described above, on the surface of a work piece comprising a rubbery material for making a seal or stamp. As apparent from the drawing, the protrusions 2 are carved perpendicularly to the machining surface according to the conventional laser machining technique to form deep notches 3 at the counters. Moreover, in some depth range, such notches become rather wider and the protrusions 2 come to have inverted trapezoidal cross sections having wider top width than the bottom width, whereby the physical strength of the protrusions 2 is reduced, making the seal or stamp to have shorter life and to be susceptible to damage, disadvantageously. In the case of a stamp made of a porous impression material used as impregnated with an ink, even supply of ink is prevented by the presence of such notches 3 to cause insufficient ink delivery.
The phenomenon that the protrusions 2 are perpendicularly carved cannot be get rid of in the conventional technique where a laser beam is irradiated perpendicularly down onto the surface of the work piece, and the control of the laser beam is achieved by on/off switching operation. It has been found that the reason why such notches 3 are formed is, as can be seen from the output characteristics of the laser oscillator shown in FIG. 11, because the momentary high power laser beam is emitted upon off-to-on switching.
On the other hand, it is well known that the shallower is the machining depth, the narrower can be the laser machining spot providing better definition. In this connection, it can be pointed out that due to the fact that seals or stamps are naturally required to have a rather deeper depth and that the definition achieved by the laser beam machining will thus be lowered, the protrusions formed thereby tend to be thinner or collapsed, disadvantageously, if the depth necessary for the seals and the like is secured.
This invention is proposed in view of the problems inherent in the conventional laser machining technique and for solving them successfully, and is directed to provide a laser beam machining process in which the protrusions to be formed on the surface of a work piece comprising a rubbery material typified by a natural rubber or elastomer by means of laser beam machining cannot be collapsed easily, and by which spread or delivery of ink and the like can be improved, and an apparatus therefor.